1. Field of the Invention
Embodiments of the present invention generally relate to methods of film deposition and, more particularly to methods of film deposition in which precursor gases are activated prior to cyclical introduction to a substrate.
2. Description of the Related Art
The deposition of thin films may be performed using any number of techniques. For many thin film applications, particularly those involving the formation of sub-micron-sized features for integrated circuits, vapor-phase deposition techniques are the most common. Vapor phase techniques include, for example, physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and cyclical chemical vapor deposition, such as atomic layer deposition (ALD).
Cyclical deposition, by which monolayers of molecules are adsorbed onto a substrate, is particularly advantageous in forming thin films with a high-degree of step-coverage and film quality, as well as a low number of defects. Cyclical deposition also enables a high degree of control over film composition, thereby enabling the formation of thin films with functionality greater than other deposition methods. In a cyclical deposition process, precursor gases are alternately introduced into a reaction chamber.
While the precise chemical composition of each precursor gas varies depending upon the desired composition of the thin film, the precursor gases must have a high degree of reactivity. Unfortunately, not all highly reactive precursor gases are practical candidates for ALD because many of these gases cause safety concerns, or are otherwise dangerous to use in an industrial process. Consequently, precursor gases with less than optimal reactivity are often used for cyclical deposition. For example, precursor gases used for cyclical deposition may be large organic molecules that have a plurality of bulky side groups or ligands. The size and number of ligands within the precursor tend to shield the active metal ions to be deposited, thereby slowing the reaction kinetics of deposition. This may result in reduced or sub-optimal coverage of the thin film causing electrical failure of a device created using these deposition techniques.
Therefore, a need exists for a method of film deposition that provides a high degree of precursor reactivity as well as improved step coverage in the film.